Cardiovascular diseases are the major causes for human death. Both the morbility and the mortality of cardiovascular diseases rank the first among all diseases. Medical studies have established that atherosclerosis is the primary pathological basis for cardiovascular diseases, and hyperlipemia is the leading factor for atherosclerosis. Therefore, the significance of lipid lowering drugs in the reduction of the incidence rate of cardiovascular diseases has attracted much attention, and researchers all over the world are dedicated to the development of lipid lowering drugs.
Among various lipid lowering drugs, a class of compounds of HMG-CoA reductase inhibitors, which were developed in the early 80's, has become the most active and rapidly developing field in studies of the cardiovascular drugs, due to their efficiency in the reduction of cholesterol levels, high selectivity for the inhibition of cholesterol synthesis, and low toxicity.
This kind of drugs are also known as statin drugs, including lovastatin, simvastatin, pravastatin, fluvastatin, cerivastatin, and atorvastatin, etc.
Compared to its analogs, pravastatin has unique tissue selectivity, selectively inhibiting the cholesterol synthesis in liver and small intestine, while only slightly inhibiting the cholesterol synthesis in other organs; furthermore, low toxicity is another advantage of pravastatin.
Pravastatin sodium (formula I) is produced from its prodrug, mevastatin (formula IIa) or mevastatin salts (formula IIb), by the hydroxylation in microorganisms.

Mevastatin (IIa) has a low water-solubility, thus commonly transformed into mevastatin salts (formula IIb, wherein, R=alkali metals (for example, Na or K), alkaline earth metals, and NH4) by adding some alkali.
In order to produce mevastatin sodium, the bio-transformation can be performed by a number of microorganisms, mainly including: some genera of the mould fungi (Mortierella, WO00/46175), Norcardiaceae (Norcardia, U.S. Pat. No. 5,830,695), Actinomycesa madurae (Actinomadura, WO96/40863), Streptomyces (Streptomyces Carbopilus EP215665, Streptomyces exfoliatus WO98/45410), and Micromonospora. 
All of the aforementioned microorganisms, however, have a disadvantage during the producing process, i.e., the prodrug (mevastatin) of pravastatin is highly toxic to these microorganisms, especially to mould fungi, thus mevastatin concentration can only be maintained at a low level during industrialized production, and the transformation rate is relatively low and dramatically increases the cost for the transformation of pravastatin by microorganism.
In large-scale industrialized production, therefore, there is an urgent demand to developing microorganisms and the corresponding processes for the production of pravastatin sodium with a high efficiency.